1. Field of the Invention
The invention relates to a vehicle light distribution control device and a vehicle light distribution control method.
2. Description of Related Art
There is known an existing technique that, in order not to cause a driver, or the like, of a vehicle ahead, such as a leading vehicle and an oncoming vehicle, to experience glare, a vehicle light distribution control device that controls the light distribution of illumination light for illuminating an area ahead of a vehicle on the basis of a vehicle ahead, detected by a camera, uses a split beam pattern in which part of an area in a high beam pattern is shielded with a boundary set at a cut-off line (for example, see Japanese Patent Application Publication No. 2011-005992 (JP 2011-005992 A) and Japanese Patent Application Publication No. 2011-063070 (JP 2011-063070 A)).
Incidentally, when a detected vehicle ahead becomes undetectable (that is, disappears), the above described vehicle light distribution control device that uses a split beam pattern is required to return the light distribution pattern from the split beam pattern to the high beam pattern. At this time, when the control device is configured to return the light distribution pattern from the split beam pattern to the high beam pattern immediately when a detected vehicle ahead becomes undetectable, chattering due to a repetition of disappearance and detection of a vehicle ahead problematically occurs as in the case where a vehicle ahead momentarily disappears and is detected again thereafter.
In contrast to this, it is also conceivable that, when a detected vehicle ahead becomes undetectable, the light distribution pattern at that point in time is maintained until a set period of time elapses and, when the vehicle ahead is still undetectable after a lapse of the set period of time, the light distribution pattern is returned from the split beam pattern to the high beam pattern.
However, with the above configuration, for a driver, the split beam pattern is maintained until the set period of time elapses although the vehicle ahead has disappeared. Therefore, this may bring a feeling of strangeness to the driver, and also may lead to a decrease in visibility.